Mechanical grating devices with electrostatic actuators are known for spatial light modulators. U.S. Pat. No. 6,307,663, which issued to Kowarz on Oct. 23, 2001, discloses a mechanical grating device for modulating an incident beam of light by diffraction. The grating device includes an elongated element having a light reflective surface. The elongated element is positioned over a substrate and is supported by a pair of end supports. At least one intermediate support is positioned between the end supports. The device also includes a means for applying a force (for example, an electrostatic force) to the elongated element to cause the element to deform between first and second operating states. U.S. Patent Application Publication No. US 2001/0024325 A1, which published in the names of Kowarz et al. on Sep. 27, 2001, discloses a method of manufacturing a mechanical conformal grating device.
Drop-on-demand liquid emission devices with electrostatic actuators are also known for ink printing systems. U.S. Pat. No. 5,644,341 and U.S. Pat. No. 5,668,579, which issued to Fujii et al. on Jul. 1, 1997 and Sep. 16, 1997, respectively, disclose such devices having electrostatic actuators composed of a single diaphragm and opposed electrode. The diaphragm is distorted by application of a first voltage to the electrode. Relaxation of the diaphragm expels an ink droplet from the device. Other devices that operate on the principle of electrostatic attraction are disclosed in U.S. Pat. No. 5,739,831, U.S. Pat. No. 6,127,198, and U.S. Pat. No. 6,318,841; and in U.S. Publication No. 2001/0023523.
U.S. Pat. No. 6,345,884, teaches a device having an electrostatically deformable membrane with an ink refill hole in the membrane. An electric field applied across the ink deflects the membrane and expels an ink drop.
IEEE Conference Proceeding “MEMS 1998,” held Jan. 25-29, 2002 in Heidelberg, Germany, entitled “A Low Power, Small, Electrostatically-Driven Commercial Inkjet Head” by S. Darmisuki, et al., discloses a head made by anodically bonding three substrates, two of glass and one of silicon, to form an ink ejector. Drops from an ink cavity are expelled through an orifice in the top glass plate when a membrane formed in the silicon substrate is first pulled down to contact a conductor on the lower glass plate and subsequently released. There is no electric field in the ink. The device occupies a large area and is expensive to manufacture.
U.S. Pat. No. 6,357,865 by J. Kubby et al. teaches a surface micro-machined drop ejector made with deposited polysilicon layers. Drops from an ink cavity are expelled through an orifice in an upper polysilicon layer when a lower polysilicon layer is first pulled down to contact a conductor and is subsequently released.
In the devices described above, the diaphragm (or membrane, etc.) is actuated (deformed and relaxed) as a whole, or an entire unit, when a drop is desired. As such, there is little control over the size of the ejected drop created during actuation of the diaphragm.